1. Field of the Invention
The present invention relates to the coupling of mechanical component parts, surfaces or assemblies and the like (hereinafter sometimes generally termed xe2x80x9ccomponentsxe2x80x9d), where low-cost, accurate, and repeatable coupling are desired, particularly in applications where the relative location of coupled components must be adjustable, yet remain repeatable after adjustment.
2. Background Information
Better precision at lower cost is a driving force in design and manufacturing. Traditionally, precision assemblies have used precision components to achieve accuracy and repeatability on the order of tens of microns. The development of next generation meso, micro and nano scale components and assemblies typically requires sub-micron accuracy and repeatability. In some cases, there may be several desirable relative positions between mated components, or time variable distortions due to thermal strain or creep that may require adjustment of the assembly interface.
While certain types of prior kinematic couplings and exact constraint couplings have been used to provide affordable sub-micron repeatability, their accuracy is subject to the manufacturing processes and design tolerances of their components. In addition, the position about which these couplings are repeatable tends to be fixed, which generally makes their use impractical in cases where the relationship between the coupled components must be varied for functional purposes or to correct time-variable misalignment errors.
This problem has been addressed in part through the use of compliant kinematic couplings as described by Slocum et al., in U.S. Pat. No. 5,678,944, which is fully incorporated herein by reference. These types of couplings kinematically locate components and then allow translation parallel to the mating direction until contact is made between the mated components. Though constituting a significant improvement over static kinematic interfaces, the operation of this coupling is not generally adjustable. The final relative location of the components relies on contacts between hard stops or contact of opposing faces of the coupled components. Once this contact is made and the coupling clamped in position, the relative location of the two components may not generally be varied. In between initial engagement and touchdown, an applied force or displacement may be used to control the relative location of the components. However, the compliance of the flexures is relatively low, which may make the coupling susceptible to errors in location due to variation in applied loads. Further, the compliance of the flexure elements may have a negative effect on the dynamic stiffness and natural frequency of the coupling.
Culpepper et al, in U.S. Pat. No. 6,193,430 entitled xe2x80x9cQuasi-Kinematic Coupling and Method for Use in Assembling and Locating Mechanical Components and the Likexe2x80x9d, and U.S. patent application Ser. No. 09/293,442 filed Apr. 16, 1999, entitled xe2x80x9cQuasi-Kinematic Coupling and Method for Use in Assembling and Locating Engine Vehicle Components and the Likexe2x80x9d, which are both fully incorporated by reference herein, employ contact between convex and concave surfaces of revolution to achieve sub-micron precision. Although this coupling is a significant advancement in that it uses the compliance of kinematic elements to achieve better accuracy through elastic averaging, it is not generally possible to achieve accuracy on the order of tens of nanometers since the effects of elastic averaging and surface finish tend to limit the couplings"" accuracy to be on the order of several microns. Further, the couplings disclosed by Culpepper et al., do not generally enable the location of coupled components to be adjusted.
Slocum, in U.S. Pat. No. 5,769,554, which is fully incorporated by reference herein, describes an apparatus and method for use in sand casting and similar applications that incorporate kinematic elements into parts of the mold in a manner that admirably solves the above stated problem, though, in general, only for relatively low precision (hundreds of microns) sand mold assemblies and the like. The use of this coupling as a means to achieve accuracy tends to be limited since the kinematic elements must be pre-formed into a static arrangement within the components. For high precision assemblies, this geometric relationship is sensitive enough that the capability of net shape manufacturing processes tends to be insufficient to provide micron-level positioning between the coupled components. While this problem may be addressed by machining the contact surfaces of the mated components, this solution tends to nullify the advantages associated with the use of pre-formed elements. Further, the static nature of such a coupling tends to inhibit assembly at different relative positions.
Taylor et al., in xe2x80x9cPrecision X-Y Microstage With Maneuverable Kinematic Coupling Mechanismxe2x80x9d, Precision Engineering, vol. 18, No. 2, April 1996, p. 85-94, describes a micro-positioning stage that utilizes an actuated kinematic interface to provide control of two linear degrees of freedom between coupled components. This coupling makes use of linear actuators to position two spheres relative to the component to which their actuator is attached. As these spheres are attached to a first component and kinematically interface with grooves in a second component, moving them relative to the first component causes relative movement between the first and second component. Due to its design, the coupling is limited to adjusting only two of six degrees of freedom. The design further limits the coupling to having the actuators oriented substantially perpendicularly to the mating direction, which tends to be undesirable as space is typically a constraint or comes at a premium along directions perpendicular to the mating direction of fixtures. In addition, this coupling achieves a ratio of input actuation motion to coupling motion that enables relatively high resolution, by orienting the direction of travel for the balls at a shallow angle to the corresponding groove""s plane of symmetry. This disadvantageously requires precision alignment between the direction of travel and the plane of symmetry. Further, with respect to manufacturing and assembly errors, the coupling described by Taylor et al., tends not to be useful for overcoming size, location, and orientation errors.
While the devices discussed in the preceding paragraphs embrace the principles of exact constraint design, a need exists for a novel design which permits a kinematic interface to be used to adjust the coupled components, thereby enabling multiple assembly combinations and/or compensation for manufacturing errors in the coupling.
In one aspect the present invention includes an adjustable kinematic coupling for providing accurate and repeatable alignment between a first component and a second component. The kinematic coupling includes a plurality of kinematic elements, including a plurality of convex elements coupled to the first component and an equal number of concave elements coupled to the second component. Each of the plurality of convex elements is configured to mate with a corresponding one of the plurality of concave elements. Further, at least one of the plurality of kinematic elements includes an axis of rotation and is rotatable thereabout. Rotation of at least one of the plurality of kinematic elements about the axis of rotation effects a change in the relative position between the first component and the second component.
In another aspect, this invention includes an adjustable kinematic coupling for removably fastening a first component and a second component to one another. The kinematic coupling includes three convex elements coupled to the first component and three concave elements coupled to the second component, with each of the three convex elements being configured to mate with a corresponding one of the three concave elements. Each of the three convex elements includes an axis of rotation and an axis of symmetry, the axis of rotation being substantially parallel to and spaced from the axis of symmetry. Further, rotation of any one or more of the three convex elements about the axis of rotation affects a change in the relative position between the first component and the second component.
In yet another aspect, this invention includes a method of removably coupling a first component and a second component to one another. The method includes disposing a plurality of kinematic elements on the first and second components, the plurality of kinematic elements including a plurality of convex elements coupled to the first component and a plurality of concave elements coupled to the second component, each of the plurality of convex elements being configured to mate with a corresponding one of the plurality of concave elements, and at least one of the kinematic elements including an axis of rotation and being rotatable thereabout. The method further includes mating the first component to the second component to establish contact between the plurality of convex elements and the plurality of concave elements, and rotating the at least one kinematic element about the axis of rotation to affect a change in the relative position between the first component and the second component.